Method to eliminate arsenic contamination in trench capacitors

ABSTRACT

A trench capacitor structure in which arsenic contamination is substantially reduced and/or essentially eliminated from diffusing into a semiconductor substrate along sidewalls of a trench opening having a high aspect ratio is provided. The present invention also provides a method of fabricating such a trench capacitor structure as well as a method for detecting the arsenic contamination during the drive-in annealing step. The detection of arsenic for product running through the manufacturing lines uses the effect of arsenic enhanced oxidation. That is, the high temperature oxidation anneal used to drive arsenic into the semiconductor substrate is monitored for thickness. For large levels of arsenic outdiffusion, the oxidation rate will increase resulting in a thicker oxide layer. If such an event is detected, the product that has been through the process steps to form the buried plate up to the drive-in anneal, can be reworked to reduce arsenic contamination.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/276,024, filed Feb. 10, 2006.

FIELD OF THE INVENTION

The present invention relates to a semiconductor structure and a methodof fabricating the same. More particularly, the present inventionrelates to a trench capacitor for use in a trench storage memory array,such as an embedded dynamic random access memory (eDRAM) array, in whicharsenic contamination is substantially reduced or essentially eliminatedfrom such structures. The present invention also relates to a method ofsubstantially reducing or essentially eliminating arsenic contaminantsfrom such semiconductor memory devices.

BACKGROUND OF THE INVENTION

A metal oxide semiconductor field effect transistor (MOSFET) is used informing dynamic random access memory (DRAM) cells. A DRAM circuittypically includes an array of memory cells interconnected by rows andcolumns, which are known as wordlines and bitlines, respectively.Reading data from, or writing data to, memory cells are achieved byactivating selective wordlines and bitlines. Typically, a DRAM cellcomprises a MOSFET connected to a capacitor. The capacitor includes twoelectrodes that are separated by a node dielectric, while the MOSFETincludes a gate and diffusion regions that are referred to as either thesource or drain region, depending on the operation of the transistor.

There are different types of MOSFETs known to those skilled in the art.A planar MOSFET is a transistor where a surface of the channel region ofthe transistor is generally parallel to the primary surface of thesubstrate. A vertical MOSFET is a transistor where a surface of thechannel region of the transistor is perpendicular to the primary surfaceof the substrate. A trench MOSFET is a transistor where a surface of thechannel region of the transistor is not parallel to the primary surfaceof the substrate and the channel region lies within the substrate. For atrench MOSFET, the surface of the channel region is usuallyperpendicular to the primary surface, although this is not required.

Trench capacitors are frequently employed with DRAM cells. A trenchcapacitor is a three-dimensional structure formed into a semiconductorsubstrate. The structure is normally formed by etching trenches having ahigh aspect ratio (a depth to width ratio of greater than 3.0) into thesubstrate. Trench capacitors commonly have N+doped polysilicon oranother conductive material as one electrode of the capacitor (i.e., thestorage node) and the other electrode of the trench capacitor is aburied plate that is formed via outdiffision of dopants, typicallyarsenic, into a portion of the substrate surrounding the lower portionof the trench.

The functionality of DRAM arrays that use deep trench storage nodesrequires the electrical isolation of the plate side of the capacitor andthe transfer device. This is accomplished using a parasitic npntransistor structure along the trench sidewall. Due to processvariability during the formation of the outdiffused buried plate,arsenic residuals can contaminate the sidewalls of the deep trench.

The arsenic residuals, in turn, counter dope the array well disposed inthe substrate after the drive-in anneal, and result in leakage of theplate charge to the transfer field effect transistor (FET) due to alower threshold voltage of the parasitic device. This problem will causefails in the writeback and signal margin tests of the cell and therebyreduce functionality and yield.

A typical prior art process of fabricating a portion of a trenchcapacitor structure is shown, for example, in FIGS. 1A-1H. Specifically,FIG. 1A shows an initial structure 10 that includes a semiconductorsubstrate 12 having at least one deep trench opening 14 located therein.The at least one deep trench opening 14 is formed by conventionallithography and etching. After etching and stripping of the photoresistmask, an arsenic doped silicate glass (ASG) layer 16 is conformallydeposited on the horizontal surfaces of the substrate 12 and on exposedwall portions of the at least one deep trench opening 14.

Next, and as shown in FIG. 1B, a photoresist 18 is then deposited on theinitial structure 10 shown in FIG. 1A. As is depicted in FIG. 1B, thephotoresist 18 is located on the ASG layer 16. The resist layer 18 fillsthe at least one deep trench opening 14 and extends on the horizontalsurface of the ASG layer 16 that is disposed above the upper surface ofthe substrate 12.

FIG. 1C shows the structure that is formed after the photoresist 18 isrecessed into a lower portion of the at least one deep trench opening 14utilizing an etching process that is selective to the photoresistmaterial. Next, an etching process is performed to recess the ASG layer16. Under ideal circumstances, this etching process is intended tocompletely remove the ASG layer 16 within the at least one deep trenchopening 14 that is not protected by the recessed photoresist 18.However, as shown in FIG. 1D, this step within the prior art processleaves residual ASG 16′ on the exposed sidewalls of the substrate 12within the at least one deep trench opening 14. The residual ASG layer16′ is typically tapered outward from the upper surface of the substrate12 at the mouth of the at least one deep trench opening 14 and extendingdown the sidewalls of the at least one trench opening 14. As such, theresidual ASG layer 16′ becomes thicker as its depth within the at leastone deep trench opening 14 increases.

Next, a dielectric cap 20 such as an oxide is formed providing thestructure that is illustrated in FIG. 1E. As shown, the dielectric cap20 is located within the at least one deep trench opening 14 and atopthe horizontal surface of the substrate 12 that extends from the mouthof the at least one deep trench opening 14. An annealing step whichdrives-in As is then performed providing the structure shown in FIG. 1F.As illustrated, the anneal step forms the n-type buried plate 22 alongan exterior bottom portion of the at least one deep trench opening 14.Additionally, and due to the presence of the residual ASG layer 16′remaining within the at least one deep trench opening 14, an As dopedregion 24 is formed within the substrate 12 along the exterior sidewallsof the at least one deep trench opening 14. As shown, this As dopedregion 24 is in contact with the buried plate 22 and it extendsvertically to the surface of the substrate 12.

FIG. 1G illustrates the structure of FIG. 1F after removing thedielectric cap 20 and stripping of the ASG layer 16 including theresidual ASG layer 16′ from within the at least one deep trench opening14. As shown, a portion of a p-well 13 along the exterior sidewalls ofthe at least one deep trench opening 14 is counter doped by the As dopedregion 24. FIG. 1H shows the structure of FIG. 1G after formation of acollar 26 and n-type diffusion regions 28.

As stated above, the presence of the arsenic residuals counter dopes thearray well after the drive-in anneal, and results in leakage of theplate charge to the transfer field effect transistor (FET) due to alower threshold voltage of the parasitic device. This problem will causefails in the writeback and signal margin tests of the cell and therebyreduce functionality and yield.

In view of the arsenic contamination problem mentioned in prior arttrench capacitor structures, there is a need for providing a trenchcapacitor structure in which such arsenic contamination is substantiallyreduced or essentially eliminated.

SUMMARY OF THE INVENTION

The prior art process of fabricating the storage node buried plateconsists of depositing an arsenic-containing film into the sidewalls ofa trench opening formed into a semiconductor substrate, and strippingthe arsenic-containing film, after arsenic has been diffused into thesubstrate by an annealing step. Due to variability in the arsenicconcentration of the film, the film thickness, the efficiency ofcleaning process to remove arsenic from the trench sidewalls, and theefficiency of the capping layer to prevent arsenic outdiffision duringthe annealing step, a high enough concentration of arsenic (on the orderof about 2×10¹⁷ atoms/cm³ or greater) can form in the array well whichmay affect device functionality.

The present invention describes the detection and subsequent method tosubstantially reduce or essentially eliminate arsenic contaminationduring the manufacturing process. The detection of arsenic for productrunning through the manufacturing lines uses the effect of arsenicenhanced oxidation. That is, the high temperature oxidation anneal usedto drive arsenic into the semiconductor substrate is monitored forthickness. For large levels of arsenic outdiffusion, the oxidation ratewill increase resulting in a thicker oxide layer. If such an event isdetected, the product that has been through the process steps to formthe buried plate up to the drive-in anneal, can be reworked to reducearsenic contamination. The rework procedure depends on the location ofthe product in the overall process flow. The advantage of the presentapplication is that product functionality and yield is protected withoutscrapping the material.

In general terms, the present invention provides a method of forming atrench capacitor which includes:

providing a semiconductor substrate having at least one trench openinghaving an aspect ratio of greater than 3.0 located therein, said atleast one trench opening having sidewalls that extend to a common bottomwall;

providing a recessed arsenic-containing film within a bottom portion ofsaid at least one trench opening, while maintaining the sidewalls in anupper portion of the at least one trench opening essentially free ofresidual arsenic; and

annealing, in an oxygen-containing ambient, to cause outdiffusion ofarsenic from said recessed arsenic-containing film into saidsemiconductor substrate, wherein during said annealing oxide growthwithin the at least one trench opening is monitored.

In accordance with the present invention, the term “essentially free ofresidual arsenic” denotes that the sidewalls of the at least one trenchopening in the upper portion thereof contain less than 5×10¹⁶ atoms/cm³arsenic.

In accordance with the present invention, the monitoring is achieved byuse of an oxide thickness monitor and the arsenic enhanced oxidationeffect. If the oxide growth exceeds a predetermined level during thisannealing step, steps are performed in the present invention to removeresidual arsenic from the at least one opening. Included within thesteps are resist apply, recess resist etch, oxide recess etch, andremoval of residual arsenic.

The present invention contemplates two embodiments of the general methoddescribed above. The two embodiments will be described in greater detailherein below.

In addition to the general method described above, the present inventionalso provides a trench capacitor structure including:

a semiconductor substrate having at least one trench opening having anaspect ratio of greater than 3.0 located therein, said at least onetrench opening having sidewalls that extend to a common bottom wall;

an arsenic-outdiffused buried plate located within said substrate aroundsaid common bottom wall of said at least one trench opening, saidarsenic-outdiffused buried plate having an outdiffused thickness ofabout 200 nm or less;

a node dielectric within a lower portion of said at least one trenchopening along said sidewalls and common bottom wall;

a collar region located on said sidewalls of said at least one trenchopening above said node dielectric, said collar region located on aportion of the semiconductor substrate that is essentially free ofarsenic contaminates; and

a conductive material within said at least one opening.

The term “essentially free of arsenic contaminates” denotes that thesemiconductor substrate abutting the collar region contains less than5×10⁻⁴% As.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1H are pictorial representations (through cross sectionalviews) depicting basic processing steps which are employed in the priorart in fabricating a portion of a trench capacitor.

FIGS. 2A-2I are pictorial representations (through cross sectionalviews) depicting a method of the present invention in accordance withone embodiment thereof.

FIGS. 3A-3E are pictorial representations (through cross sectionalviews) depicting a method of the present invention in accordance withanother embodiment thereof.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which provides a method to substantially reduceor essentially eliminate arsenic contamination along sidewalls of atrench capacitor structure and the resultant trench capacitor structureformed thereby, will now be described in greater detail by referring tothe following description and drawings that accompany the presentapplication.

Reference is first made to FIGS. 2A-2I which are cross-sectional viewsof the inventive trench capacitor structure through a first embodimentof the present invention. The first embodiment of the present inventionbegins by fabricating the initial structure 50 shown in FIG. 2A. Asillustrated, the initial structure 50 shown in FIG. 2A includes asemiconductor substrate 52 having at least one trench opening 54 (i.e.,one or more trench openings) having a high aspect ratio located therein.The term “high aspect ratio” denotes the at least one trench opening 54has a depth to width ratio of greater than 3.0, preferably greater than5.0. The initial structure 50 also includes an arsenic-containing film56 which is located within the at least one trench opening 54 andextending atop a surface of the semiconductor substrate 52.

The term “semiconductor substrate” is used throughout the presentapplication to denote any material having semiconducting properties.Suitable examples of such semiconducting materials include, but are notlimited to: Si, SiGe, SiC, SiGeC, Ge alloys, GaAs, InAs, InP as well asother III/V or II/VI compound semiconductors. The semiconductorsubstrate 52 may also comprise a layered semiconductor such as, forexample, Si/SiGe, or a semiconductor-on-insulator. Typically, thesemiconductor substrate 52 is a Si-containing semiconductor such as, forexample, Si, SiGe, SiC, SiGeC, a silicon-on-inuslator or aSiGe-on-insulator. Preferably, the semiconductor substrate 52 is asilicon substrate.

The semiconductor substrate 52 can be in a crystalline, polycrystallineor amorphous form. The semiconductor substrate 52 may comprise a singlecrystal orientation or it may comprise surface regions that havedifferent crystal orientations. The later substrates are referred to ashybrid orientation substrates (i.e., HOT substrates).

The semiconductor substrate 52 may be of the n- or p-type depending onthe type of device to be fabricated. Moreover, the substrate 52 maycontain various isolation and/or device regions formed within thesubstrate 52 or disposed thereon. For clarity, these regions are notshown in the drawings, but are nevertheless meant to be included withinregion 52.

Next, at least one trench opening 54 having a high aspect ratio is thenformed into the semiconductor substrate 52. The at least one trenchopening 54 is formed utilizing standard techniques that are well knownin the art. For example, an optional hardmask (not shown) can be firstformed onto the surface of the substrate 52 utilizing a standarddeposition process such as, for example, chemical vapor deposition(CVD), plasma enhanced chemical vapor deposition (PECVD), sputtering,chemical solution deposition, evaporation or atomic layer deposition.Alternatively, the optional hardmask can be formed utilizing a thermaloxidation, nitridation or oxynitridation process. Combinations of thesetechniques are also contemplated herein. The optional hardmask, which isdisposed on the surface of the semiconductor substrate 52, may becomprised of an oxide, nitride, oxynitride, silicate glass material orany combination thereof Examples of hardmasks that can be employed inthe present invention include, but are not limited to: ones that arecomprised of silicon dioxide and/or silicon nitride. The thickness ofthe optional hardmask may vary depending, for example, on the techniqueused in forming the same and the number of material layers within thehardmask. Typically, the optional hardmask has a thickness from about500 to about 3000 nm.

A photoresist mask, not shown, is then formed atop the surface of theoptional hardmask (or atop substrate 52, when no hardmask is employed)utilizing a conventional deposition process and thereafter thephotoresist mask is patterned utilizing conventional lithography whichincludes exposing the photoresist to a pattern of radiation, anddeveloping the pattern into the exposed photoresist utilizing aconventional resist developer. After the photoresist has been patterned,the pattern is transfer into the optional hardmask and substrate 52utilizing a conventional dry etching process such as reactive-ionetching, plasma-etching, ion beam etching, laser ablation or anycombination thereof so as to form the at least one trench opening 54 inthe substrate 52. The depth of the at least one trench opening 54,measured from the uppermost surface of substrate 52 is typically fromabout 0.1 to about 10 μm, with a depth of from about 5 to about 10 μmbeing more highly preferred. The width of the at least one trenchopening 54 is typically from about 100 to about 500 nm, with a widthfrom about 100 to about 400 nm being even more typical. It is noted thatthe above ranges provide at least one trench opening 54 that has a highaspect ratio.

Note that each of the trench openings 54 formed has vertical sidewallsthat extend to a common bottom wall. The bottom wall may be curved asshown in the drawings, or it may be substantially horizontal.

Following the formation of the at least one trench opening 54, thephotoresist is removed utilizing a conventional stripping process wellknown to those skilled in the art. At this point of the inventiveprocess the optional hardmask is also removed utilizing a conventionalwet chemical strip process such as hydrofluoric-sulphuric acid.

Next, an arsenic-containing film 56 is formed on the exposed surface ofthe substrate 52 including within the at least one trench opening 54.The arsenic-containing film 56 within the at least one trench opening 54covers the bare sidewalls and the bottom wall of the at least one trenchopening 54. The arsenic-containing film 56 is formed utilizing a.conventional conformal deposition process such as, for example, chemicalvapor deposition, plasma enhanced chemical vapor deposition, sputtering,atomic layer deposition, chemical solution deposition and the like. Thearsenic-containing film 56 is typically an arsenic doped silicate glass(i.e., arsenic-doped silicate glass, ASG) or another like sacrificialdielectric material that includes arsenic in a sufficient concentrationwhich is capable of forming a buried plate within the substrate 52during a subsequent annealing step. The concentration of arsenic withinthe arsenic-containing film 56 may vary so long as the amount issufficient to form a buried plate within the substrate. Typically, thearsenic-containing film 56 has an arsenic concentration from about1×10²¹ to about 2×10²² atoms/cm³, with a range from about 1×10²² toabout 1.5×10²² being more typical.

The arsenic-containing film 56 is a continuous film whose thicknessalong the sidewalls and common bottom wall within the at least onetrench opening 54 is typically uniform. By ‘uniform” it is meant thatthe thickness variation of the arsenic-containing film 56 is less than 4nm. Typically, the arsenic-containing film 56 has a thickness from about5 to about 40 nm with a thickness from about 5 to about 30 nm being evenmore typical.

Next, and as shown in FIG. 2B, a first photoresist 58 is formed on thestructure shown in FIG. 2A. As is illustrated, the photoresist 58 isformed within the at least one trench opening 54 atop of the previouslyformed arsenic-containing film 56 as well as atop the arsenic-containingfilm 56 that extends above the at least one trench opening 54. Thephotoresist 58 comprises any conventional photoresist or ananti-reflective coating material, and it is formed utilizing aconventional deposition process, including, for example, spin-oncoating, CVD, and PECVD.

After forming the photoresist 58, the photoresist 58 is recessedutilizing an etching process such that a recessed photoresist 58′remains in a bottom portion 60 of the at least one trench opening 54.Typically, the photoresist 58 is recessed to a predetermined level(typically about 2 μm or less) beneath the upper surface of substrate52. The resultant structure including the recessed photoresist 58′ isshown in FIG. 2C. The etching process used in forming the structureshown in FIG. 2C comprises an etching process that is selective forremoving the photoresist material from a top portion 62 of the at leastone trench opening 54. Typically, the etching process is a timedreactive-ion etching process wherein the etch chemistry is selective inremoving photoresist material.

FIG. 2D illustrates the structure of FIG. 2C after the exposedarsenic-containing film 56 in the top portion 62 of the at least onetrench opening 54 is recessed utilizing a conventional etching processthat is selective in removing the arsenic-containing film 56 that is notprotected by the recessed photoresist. Due to the etch chemistries andother variables, residual arsenic-containing film 56′ remains on thesidewalls of the at least one trench opening 54 in the top portion 62thereof As is illustrated, the thickness of the residualarsenic-containing film 56′ tends to be less the further it gets fromthe arsenic-containing film 56 in the bottom portion 60 of the at leastone trench opening 54.

After recessing the arsenic-containing film 56, the recessed photoresist58′ is removed from the bottom portion 60 of the at least one trenchopening 54 utilizing a conventional stripping process that is well knownto those skilled in the art. After stripping the recessed photoresist58′ from the at least one trench opening 54, the arsenic-containing film56 and the residual arsenic-containing film 56′ are both exposed.

FIG. 2E illustrates the structure after a first dielectric cap 64 isformed. As shown, the dielectric cap 64 is formed within the at leastone trench opening 54 on the exposed surfaces of the arsenic-containingfilm 56 and residual the arsenic-containing film 56′. The dielectric cap64 is comprised of an oxide, nitride, oxynitride, or any combinationthereof, with oxide dielectrics being high preferred. The dielectric cap64 is formed utilizing a conventional deposition process such as, forexample, CVD, PECVD, evaporation or chemical solution deposition. Thedielectric cap 64 has a uniform thickness (with little or no thicknessvariation) from about 10 to about 100 nm, with a thickness from about 30to about 90 nm being highly preferred.

After forming the dielectric cap 64, a second photoresist 66 is formedfilling the at least one trench opening 54 and extending atop thedielectric cap 64 that was previously formed atop the substrate 52. Thesecond photoresist 66 is formed utilizing the same or differentdeposition process as the first photoresist 58 and it comprises a sameor different photoresist material as that of the first photoresist 58.The resultant structure including the second photoresist 66 is shown,for example, in FIG. 2F.

FIG. 2G shows the structure after the second photoresist 66 has beenrecessed forming a recessed second photoresist 66′ within the bottomportion 60 of the at least one trench opening 54. The recessing of thesecond photoresist 66 is performed utilizing an etching process asdescribed above for recessing the first photoresist 58. The recessedsecond photoresist 66′ has a height that is substantially the same asthat of the remaining arsenic-containing film 56 within the bottomportion 60 of the at least one trench opening 54.

Next, the exposed dielectric cap 64 within the upper portion 62 of theat least one trench opening 54 is removed utilizing an etching processthat selectively removes that dielectric material. During this etchingprocess, the residual arsenic-containing film 56′ is also removed suchthat bare semiconductor sidewalls are present in the upper portion 62 ofthe at least one trench opening 54. The etching process performed atthis point of the present invention typically comprises a reactive-ionetching process where the etch chemistries are selective in removingdielectric material. After providing the bare sidewalls within the upperportion 62 of the at least one trench opening 54, the recessed secondphotoresist 66′ is stripped utilizing a conventional removal processwhich exposes the underlying dielectric cap 64 in the bottom portion 60of the at least one trench opening 54. This ‘remaining’ dielectric cap64 may optionally be removed utilizing an etching process selective forremoving the dielectric material, or it can remain in the trenchopening. The former is shown in the drawings of the present invention. Asecond dielectric cap 68 is the formed providing the structure shown,for example, in FIG. 2H. It is noted that during the various etchingprocesses mentioned in providing the structure shown in FIG. 2H, thearsenic-containing film 56 can be recessed further down within the atleast one trench opening 54.

At this point of the present invention, arsenic from the remainingarsenic-containing film 56 is outdiffused into the semiconductorsubstrate 52 forming a buried plate region 70 that is doped witharsenic. The buried plate region 70 has an arsenic dopant concentrationfrom about 1×10¹⁸ to about 1×10¹⁹ atoms/cm³, with a dopant concentrationfrom about 5×10¹⁸ to about 1×10¹⁹ atoms/cm³ being more typical.Additionally, the buried plate region 70 has a diffusion thickness thatis less than 200 nm. The outdiffusion is performed utilizing anannealing step in which an oxygen-containing ambient such as O₂, NO,ozone or the like is used. The annealing step is performed at atemperature of about 800° C. or greater.

After the anneal step, the second dielectric cap 68 is selectivelyrecessed utilizing conventional processing from the least one trenchopening 54. The arsenic-containing film 56 is then removed utilizing aconventional stripping process and thereafter the node dielectric 74, aconductive material 76, and a collar 72 are formed utilizingconventional techniques providing the structure shown, for example, inFIG. 2I. The node dielectric 74 is comprised of any conventionaldielectric material including for example, oxides, nitrides, oxynitridesor combinations thereof. Typically, the node dielectric 74 is an oxidesuch as, for example, SiO₂, Al₂I₃, Ta₂O₅, HfO₂, La₂O₃, perovskite typeoxides, or any combination thereof, including multilayers. Conductivematerial 76 is typically comprised of doped polysilicon, doped SiGe, aconductive metal, a conductive metal nitride, a conductive metalsilicide, or any combination thereof. It is noted that in FIG. 2I,diffusion regions 78 are shown in the substrate adjacent the upperportion 62 of the at least one trench opening 54. The collar 72 maycomprise an oxide or nitride, with oxides being highly preferred. Thediffusion regions 78 are form utilizing conventional processing wellknown to those skilled in the art.

Further processing steps to form a MOSFET, which are well known to thoseskilled in the art, can now be performed in providing a DRAM cell.

Reference is now made to FIGS. 3A-3E which illustrate the inventivestructure through a second embodiment of the present invention. Thesecond embodiment of the present invention begins by first providing thestructure shown in FIG. 3A. It is noted that this structure shown inFIG. 3A is the same as that shown in FIG. 2E and, as such, theprocessing steps described above in forming the structure shown in FIG.2E are also used herein in forming the structure shown in FIG. 3A.

Next, the dielectric cap 64 and the residual arsenic-containing film 56′are removed from the structure utilizing an etching process thatselectively removes these materials. During this step, the remainingarsenic-containing film 56 is recessed further down within the at leastone trench opening 54 and typically it is thinned during theseprocessing steps. A second dielectric cap 68 is then formed as describedabove providing the structure shown, for example, in FIG. 3B.

With the second dielectric cap 68 in place, the above describedannealing process is performed which causes outdiffusion of arsenic fromthe arsenic-containing film 56 into the substrate 52 forming buriedplate region 70. The buried plate region 70 formed during this step ofthe present invention has a lower arsenic concentration than that of theburied plate region 70 formed in the first embodiment of the presentinvention. Typically, the buried plate region 70 formed in the secondembodiment of the present invention has an arsenic concentration of lessthan 9×10¹⁸ atoms/cm³. The thickness of the outdiffusion in this secondembodiment is less than that of the first embodiment. Typically, and forthe second embodiment, the buried plate region 70 has an outdiffusedthickness of about 100 nm or less. The resultant structure, includingthe buried plate region 70 is shown, for example, in FIG. 3C.

FIG. 3D shows the structure of FIG. 3C after stripping the seconddielectric cap 68 and stripping the remaining arsenic-containing film56. These steps of the present invention are the same as that discussedabove for the first embodiment.

FIG. 3E illustrates the structure after formation of the node dielectric74, a conductive material 76, collar 72 and diffusion regions 78. Theseelements and regions are formed utilizing conventional techniques thatare well known in the art.

It is submitted that the various processing embodiments mentioned above,provide a trench capacitor structure in which the arsenic outdiffusioninto the sidewalls of the trench opening in the upper portion thereofthat abuts the collar is substantially reduced or essentiallyeliminated. Thus, the concentration of arsenic that would be present inthe array well is low (on the order of less than 5×10¹⁶ atoms/cm³). Atsuch low arsenic levels, the functionality of the device is notnegatively impacted.

It is further noted that that during the drive-in anneal mentionedabove, the present invention detects the arsenic contamination andprovides means for eliminating the same therefrom. In particular, thehigh temperature oxidation anneal used to drive arsenic into thesemiconductor substrate is monitored for thickness. For large levels ofarsenic outdiffision, the oxidation rate will increase resulting in athicker oxide layer. If such an event is detected, the product that hasbeen through the process steps to form the buried plate up to thedrive-in anneal, can be reworked to reduce arsenic contamination. Therework procedure depends on the location of the product in the overallprocess flow. The advantage of the present application is that productfunctionality and yield is protected without scrapping the material.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A method of fabricating a semiconductor structure comprising:providing a semiconductor substrate having at least one trench openinghaving an aspect ratio of greater than 3.0 located therein, said atleast one trench opening having sidewalls that extend to a common bottomwall; providing a recessed arsenic-containing film within a bottomportion of said at least one trench opening, while maintaining thesidewalls in an upper portion of the at least one trench openingessentially free of residual arsenic; and annealing in anoxygen-containing ambient to cause outdiffusion of arsenic from saidrecessed arsenic-containing film into said semiconductor substrate,wherein during said annealing oxide growth within the at least onetrench opening is monitored.
 2. The method of claim 1 wherein saidproviding said semiconductor substrate having said at least one trenchopening comprises lithography and etching.
 3. The method of claim 1wherein said providing said recessed arsenic-containing film comprisesforming an arsenic-containing film within the at least one trenchopening covering said sidewalls and said bottom wall, forming a firstphotoresist within said at least one trench opening on saidarsenic-containing film, recessing said first photoresist to exposeportions of the arsenic-containing film in the upper portion of the atleast one trench opening, and entirely removing said arsenic-containingfilm from said upper portion of said at least one trench opening.
 4. Themethod of claim 3 wherein said entirely removing said arsenic-containingfilm comprises recessing said arsenic-containing film from said upperportion whereby a residual arsenic-containing film remains, forming afirst dielectric cap within said at least one trench opening andstripping said first dielectric cap and said residual arsenic-containingfilm from said at least one trench opening.
 5. The method of claim 1wherein said annealing is performed at a temperature of 800° C. orabove.
 6. The method of claim 1 wherein said oxygen-containing ambientcomprises one of O₂, NO or ozone.
 7. The method of claim 1 wherein saidmonitoring includes an oxide thickness monitor.
 8. The method of claim 1further comprising forming a trench dielectric, a conductive materialand a collar region within said at least one trench opening, whereinsaid trench dielectric is located between said conductive material andsaid outdiffused arsenic.
 9. The method of claim 1 wherein saidundiffused arsenic forms a buried plate of a trench capacitor that hasan outdiffused thickness of about 100 nm or less.
 10. The method ofclaim 4 wherein said outdiffused arsenic forms a buried plate of atrench capacitor that has an arsenic concentration of less than about9×10¹⁸ atoms/cm³.